In prior U.S. Pat. Nos. 3,842,647, 3,902,288 and 3,967,430 of the same inventor as the present invention, there are disclosed a shaped panel characterized by parallel sidewall portions that are perpendicular to an intermediate wall portion and a flange that extends directly laterally out from the upper extremities of the sidewall portions so that assembled panels have sidewall portions that fit flush against one another.